The Horten Brothers’ Jet Flying Wing
by Stephan Wilkinson / 1/30/2019
“Reimar Horten and his older brother Walter were German aircraft homebuilders. Their relatively short aircraft-building careers extended from 1933 until the end of World War II, though they did some minor work in Argentina after the war as expatriate Nazis. Had they lived 40 years later, chances are they would have been busy members of an EAA chapter in Germany, making a living selling kits for their high-performance flying-wing sailplanes.
The Hortens weren’t Burt Rutans. Talented, yes, but not the aeronautical geniuses they’ve been called by some. They built a series of increasingly sophisticated iterations of the same basic design—graceful sweptwing, tailless gliders, though several of their wings were powered.
The Hortens produced a grand total of 44 airframes of their dozen basic designs. History has portrayed them as aeronautical visionaries, for in 1940 Messerschmitt Me-109 pilot Walter Horten, who scored seven Battle of Britain victories as Adolf Galland’s wingman, proposed putting a pair of Germany’s new axial-flow jet engines into a Horten glider. The result was the Ho IX. Brother Reimar was the aerodynamicist and designer; Walter was the facilitator, eventually holding an important Luftwaffe position that allowed him to divert government supplies, staff and facilities for his brother.
The jets were first going to be two BMW 003s, but when they underperformed the Hortens switched to Junkers Jumo 004Bs. The Ho IX V2 (Versuch 2, or Test 2—the V1 was an unpowered research glider) officially flew three times, crashing fatally at the end of the third flight when one of its two Jumos failed.
“The first of two H IILs built in Lippstadt in 1937 was flown by Reimar Horten at a glider contest.”
No Horten IX ever flew again, but the brothers had undeniably built and tested the world’s first turbojet flying wing. The Ho IX V2 first flew in March 1945, more than 3½ years before Northrop’s eight-jet YB-49 flying-wing bomber took off. In a number of ways, the Hortens were well ahead of Jack Northrop and his engineers, though Northrop never admitted that. After the war, it was suggested to Northrop that he hire the brothers. “Forget it, they’re just glider designers,” he said condescendingly. The success of the Ho IX was pointed out to him, but Northrop dismissed it as a Gotha design, not a Horten.
Northrop was wrong, but the source of his confusion was the fact that the Luftwaffe, knowing the tiny Horten garage operation could never mass produce twin-engine jet fighter-bombers, turned the project over to Gotha, a large railroad car manufacturing company with aircraft-building experience. As a result, the Horten jet has come down to us with a confusing suite of names. The actual sole jet-powered wing that flew was the Ho IX V2. The German air ministry (Reichsluftfahrtministerium, or RLM) gave the project an official make and model designation—Ho-229. Because production was assigned to Gotha, some sources still refer to the airplane as a Go-229.
Many Luftwaffe aircraft were built by a variety of manufacturers, but a Junkers remained a Ju, a Heinkel an He, a Dornier a Do no matter who actually manufactured it, so “Go-229” is a misnomer. The Smithsonian’s National Air and Space Museum, citing the RLM designation, calls a major artifact in its collection that is about to undergo serious conservation a Horten 229. This despite the fact that no production Horten 229 ever existed; what the Smithsonian has is the never-completed Ho IX V3 built by Gotha.
It bears mentioning that neither Northrop nor the Hortens invented flying wings. Both the concept and actual flying wings have been around since the 1910s. In fact, by the late 1920s there had been enough experiments with flying wings that the configuration was considered passé, and both Jack Northrop and the Hortens were late to the party.
“The Horten Ho 229, the world’s first jet-powered flying wing”
The Hortens have also been credited with designing and building the world’s first stealth fighter. That is a more difficult claim to support. It’s a popular fiction in the “Hitler’s wonder weapons” community, and it got a boost in a 2009 Northrop Grumman–sponsored film, Hitler’s Stealth Fighter, a National Geographic documentary. The doc tried to show that a modern replica of the National Air and Space Museum’s Ho IX V3 bombarded by microwaves revealed moderate radar-deflecting properties. Northrop Grumman’s prototyping shop built the replica for $250,000. That’s a bargain for an hour-long video broadcast on the History Channel that is still being discussed by what some call the “Napkinwaffe”—a dig at where the plans for some of the Luftwaffe’s fantasy fighters were first sketched. (Engineering drawings for the Horten jet reveal this to be not far from the truth.)
“Test pilot Erwin Ziller starts the Ho IX V2’s engines at Oranienburg in February 1945. Ziller was killed when the V2 lost an engine and crashed during its third test flight.” (National Air and Space Museum)
Northrop Grumman built the Horten replica entirely of wood, its plywood skins layered with radar-absorbent carbon-impregnated glue. Only the externally radar-visible instrument panel backing and first-stage compressor disks were metal. Yet the Horten brothers’ original airplane also had an 11-foot-wide center section made of welded steel tubing, and it carried two turbojet engines. Neither of these were part of the Northrop Grumman replica. It could be argued that all this metal might have reflected at least some microwave energy that penetrated the plywood. But Northrop Grumman felt that their special glue made the replica totally opaque to radar.
The replicators also left out the original Ho IX V3’s eight large aluminum fuel tanks. Nor did Northrop Grumman include the underwing bombs that would have been necessary for any attack on a radar-defended target. Externally racked ordnance destroys any semblance of stealth. The Nat Geo film ended up suggesting that an all-wood Horten might have been able to do a fly-by of Britain’s by then obsolete Chain Home low-frequency radar array, but it wouldn’t have been able to bomb anything.
Narration over the film says that it reveals “just how close Nazi engineers were to unleashing a jet that some say could have changed the course of the war.” Not bloody likely, if only because by that time, the Germans were literally out of gas.
The heart of the Horten stealth assertion is a claim by the brothers, made long after the war ended, that they indeed had intended to fasten the layers of the Ho-229’s plywood sheathing with glue mixed with radar-absorbing charcoal. Perhaps they did mean to do that, but the first mention of this plan came in a 1983 book written by Reimar, at a time when the basics of U.S. stealth technology were becoming public knowledge. There is no mention of any attempt to achieve stealthy properties for the Ho-229 by anybody involved in the actual fabrication of the prototypes.
NASM’s restoration facility ran extensive digital-microscopy, X-ray diffraction and Fourier-transfer spectroscopy tests on the wooden structure of their Horten aircraft’s wing and found no evidence of any carbon or charcoal impregnation of the glue. The black specks that Northrop Grumman had assumed were evidence of the Hortens’ attempt to create a radar blanket were found to be simply oxidized wood.
Reimar Horten originally planned to sheathe the Ho IX in aluminum, which hardly suggests that he had stealth as an objective. It was only when he discovered to his surprise that the Messerschmitt Me-163 rocket plane was covered in plywood that he realized high speed didn’t rule out using wood. He then switched to more easily obtainable plywood veneer, but for reasons that had nothing to do with its radar attenuation and everything to do with its availability.
It’s also worth noting that the Ho-229 was intended to be a day fighter, a bomber interceptor, though eventually, as was true of so many Luftwaffe fantasy fighters, it was to undertake a variety of other roles. Walter Horten had originally advocated jet power because, as a fighter pilot himself, he wanted to build a better airplane than the Focke Wulf Fw-190, which he considered to be an inferior, spin-prone design.
So why would stealth have been a criterion, if an Ho-229 would never confront radar? It wasn’t. Hitler’s “stealth fighter” was simply intended to be Hitler’s aerodynamically efficient, fast, maneuverable fighter. How did the Hitler’s stealth fighter myth take root? Certainly there’s fertile ground upon which such legends can be sown among the model builders and war gamers who love nothing more than mysterious Luftwaffe wonder weapons that would have reversed the course of the war had it only lasted another month. But none seem to understand the years-long prototyping/testing/production process that is a necessary part of bringing a sophisticated aircraft from napkin sketch to combat. Exactly three years and a day passed between the Messerschmitt Me-262 twin-jet’s first flight and the beginning of its operational readiness. Following such a schedule, the Ho-229 would have been ready for combat in early 1948.
The Ho IX, precursor of the 229, was the work of a garage shop. The V1 and V2 versions were built in what was essentially a three-car workshop, out of largely unairworthy structural material. The center section steel tubing was much like what today suffices for building trade electrical conduit, and the Hortens were notorious for using household-grade plywood veneer for their airplanes’ external sheathing.
How professional were the Hortens? Some of their work raises questions. Walter Horten was assigned the job of calculating the V2’s center of gravity, for example, which he did using a steel measuring tape. Unfortunately, he never noticed that the first 10 centimeters of the tape had broken off, so his false measurements determined that the airplane needed substantial ballast in the nose. Since the CG was 10 centimeters off, the test pilot assigned to the first flight found that he could barely keep the airplane aloft with full back stick, and when he tried to flare for landing the airplane hit so hard that it badly damaged the gear. And the Hortens’ fabricators welded and rewelded the V2’s center section as the engine choice flip-flopped between BMW and Junkers, which created heat stresses that no experienced aircraft builder would have allowed. Skilled welders would have cut out and rebuilt entire sections of the structure.
The Hortens also needed to adapt cast-off components to their Ho IX airframe, which led to its ungainly nosewheel. The airplane’s main gear is fashioned from Me-109 parts, and the enormous nosewheel, almost 5 feet in diameter, is the tailwheel, tire and retraction mechanism from a Heinkel He-177 Greif, a benighted heavy bomber. It was a fortuitous choice nonetheless. The oversize nosewheel put the Ho IX at a 7-degree angle of incidence at rest, which facilitated takeoff without requiring the forceful rotation other Horten designs had needed.
After the war, a number of Horten designs were examined by the Allies, initially the British. If any conspiracy theorists noticed the byline at the beginning of this article, they’ll by now be hyperventilating, for the “Wilkinson Report,” written by a committee of British aviation authorities headed by soaring expert Kenneth Wilkinson, was supposedly highly critical of the Hortens. (If Kenneth and I are related, it is to the same degree that Henry and Harrison Ford are.)
British aviation writer Lance Cole, apparently a serious Horten conspiracist, wrote that the Wilkinson Report was “a way of helping to shield the reality of the Horten achievement so that greater powers could seize the ideas and keep them unseen for decades…[it] dismissed their ideas and works as apparent flights of fancy; stemming, it seemed, from what felt like a British attitude of the Hortens being men ‘without the proper background.’”
I can find none of this in the evenhanded, rigorous, authoritative, technical 60-page Wilkinson Report. The paper does point out that British engineers tended to trust wind-tunnel data more than they did inflight assessments, but admits the Hortens had no access to such a tunnel. It calls the Hortens’ careers “a remarkable record of progress in spite of [such] obstacles.”
One thing that did baffle Wilkinson’s committee was that so little of Reimar Horten’s work was of the slightest use to the German war effort. Reimar was far more interested in record-setting and competition gliders, and he continued to design and build them throughout the war. Some historians, in fact, think that he viewed the jet wing as a “flying résumé” that would help him get a job in the U.S. or Britain after the war. Reimar would have loved to carry on his career in the States. Despite membership in the Nazi Party and his work as a Luftwaffe assault-glider instructor, he had first tried to emigrate to America in 1938 but had been refused an exit visa since he was thought to have had access to classified information.
Why a flying wing? What’s wrong with the conventional designs that have served so well since the early 1900s? Certainly there have been some useful variations—canards, pushers, semi-tailless deltas, blended wing/body proposals, even Vincent Burnelli’s perennial lifting-fuselage concept—but the pure flying wing has always been an outlier. What is its appeal?
Theoretically, the advantages of a flying wing are substantial. A conventional design—a Boeing 777, a Cessna Skyhawk, an F-22 Raptor, you name it—has wings that contribute lift despite inevitable induced and parasitic drag…plus a fuselage, engine nacelle(s) and an empennage that contribute nothing but drag. Zero lift. Indeed a conventional horizontal stabilizer often adds negative lift—downforce—to an airplane. Yes, the fuselage can carry passengers, cargo or ordnance, but so can a flying wing.
One of the major functions of a fuselage is to support the empennage that provides pitch and yaw control for a conventional airplane. A flying wing totally eliminates the drag of an aft fuselage and empennage. In fact, every part of a flying wing is a lifting surface.
An all-wing aircraft also allows for the efficiency of span-loading. Much of a conventional airplane’s weight is concentrated near its centerline, hence the videos of bendy-wing Boeing Dreamliners looking as though they’re trying to clap hands above their fuselages. The forces concentrated at the wing/fuselage juncture of a conventional airplane are enormous, while a flying wing can spread the entire load from wingtip to wingtip, thus allowing for a lighter and more efficient structure.
The weight is spread out where the lift is, so a flying wing can have a large, efficient, high-aspect-ratio span without requiring a heavy framework to support it.
For a stealthy airplane, a true flying wing has a distinct advantage: It does away with all radar-reflective vertical surfaces, particularly stabilizers and rudders. This, plus its wooden construction and lack of radar-reflecting prop discs, is what gave Northrop Grumman’s Ho IX replica its comparatively small radar cross-section, not a miracle glue.
The disadvantage of a flying wing is its natural instability, with no tail to provide counterbalance in pitch and yaw. The Hortens overcame much of this with enlightened wing, airfoil and control-surface design, but their airplanes still exhibited the classic flying-wing waddle, semi-technically termed Dutch roll. The Ho IX V2’s flights had already revealed moderate lateral instability. It would have made the Ho-229 a dreadful gun platform as a fighter and a handful as a bomber. (This was the characteristic that doomed the Northrop YB-49 flying wing in its competition with what became the Convair B-36; bomb-run accuracy was impossible to achieve when yaw/roll coupling determined the meandering flight path. Nor did it help that one YB-49 went out of control and crashed fatally during stall testing in June 1948.)
By the time Gotha took over the Ho-229 project, the Horten brothers had lost interest and moved on to their planned masterpiece—a six-turbojet flying wing “Amerika Bomber.” The Ho XVIII never was built, but it filled another niche in the Napkinwaffe. Some still say the Amerika Bomber (several German airframers were racing to build one) was intended to drop an atomic bomb on New York. Fortunately, the Germans would never have been able to build such a weapon, having lost their Norwegian deuterium source, but they did have the capability to put together a dirty bomb—a large conventional bomb encased in strongly radioactive material that would have polluted a wide area with radiation.
Though Northrop wanted nothing to do with the Horten brothers, the company did acquire several of their gliders for research after WWII, leading conspiracists to claim that Northrop stole the Hortens’ secrets for its own flying wings. Actually, Northrop depicted an Ho VI glider in postwar aviation magazine ads as an example of “one of the Nazi attempts to adapt U.S. flying-wing design for eventual military use.”
The Smithsonian’s Ho IX V3 was brought to America as part of Operation Seahorse, a U.S. Navy counterpart to the better-known Operation Paperclip campaign to acquire as many interesting Luftwaffe aircraft as possible. But it was never flown and in fact was only half-completed. It was first assessed at the Royal Aircraft Establishment, in Britain—the source of the Wilkinson Report data—and was then sent to both Wright and Freeman fields for Army Air Forces scrutiny. The jet wing ended up stored outdoors in Chicago at a facility that was intended to become a national air museum. In 1952 the Smithsonian acquired the airplane, though it was by then badly beaten up by numerous moves and exposure to the weather. It was moved once more to “a secret government warehouse,” according to published reports. That warehouse was actually the Smithsonian’s quite unsecret Suitland, Md., restoration facility, where it stayed for 60-plus years, part of that time stored in an open wooden shed.
The artifact is in sad shape today, much of its plywood sheathing delaminated and rotting, its metal frame and landing gear corroded, and parts missing. NASM has it on the short list for major work, and the V3 can currently be seen at the museum’s restoration facility in the Udvar-Hazy Center at Dulles Airport.
That work will not be restoration but conservation: stopping the rot and corrosion, cleaning up the airframe and assembling the center section and outer wings into a single unit. Those wings may or may not have been part of the V3. Only one wing came to the U.S. with the center section, and another was later found some distance from the Gotha shop.
The Hortens’ last hurrah took place without their participation. In July 1947, there was a notorious occurrence at Roswell, N.M, known forever after as the “Roswell Incident.” It allegedly involved the crash of a flying saucer and the snatching by the Army Air Forces of the bodies of three aliens aboard it. The Roswell Incident engendered decades’ worth of tabloids portraying the gourd-headed ETs perhaps still stored in freezers in a heavily guarded Area 51 hangar. The government tried to explain away the crash by saying it had been a high-altitude weather balloon; it was actually a secret surveillance balloon intended to keep track of Soviet atomic bomb testing. But some observers with more specialized knowledge had an intriguing theory.
In 1937 Reimar Horten decided that the ultimate flying-wing shape would be a parabola—a wing with a near-circular leading edge planform, which would provide the minimum induced drag and maximum lift. The Hortens built just one parabola-wing glider but never flew it; the airplane was torched after warping and becoming unglued during winter storage. But wait, there’s more…supposedly the AAF found out about the Horten parabola wing and decided to build a powered version to secretly test Reimar’s theory. It was this airplane, looking uncannily like two-thirds of a flying saucer, that crashed in New Mexico in 1947. Nobody has yet explained the aliens, however.”
For further reading, contributing editor Stephan Wilkinson recommends: The Horten Brothers and Their All-Wing Aircraft, by David Myhra; and Horten Ho 229 Spirit of Thuringia: The Horten All-Wing Jet Fighter, by Andrei Shepelev and Huib Ottens. This feature originally appeared in the November 2016 issue of Aviation History Magazine.
JET FLYING WING
Two brothers, one wing
by Philippe Ballarini / translation: Mike Leveillard
“Before evoking the story of the Horten brothers and their strange machines, a review of some background is necessary. As used as we are to visualize a traditional airplane with a fuselage, we are somewhat taken abashed when looking at a flying wing, and yet, its concept dates back from the dawn of aviation. The benefits of a flying wing become easy to understand when we consider that the fuselage and the tail section produce 30% to 50% of an airplane’s drag, thus the reason that purists such as Lippisch or Northrop pursued this concept. The idea of a flying wing is far from being a novelty; it made its appearance at the birth of aviation, and it was a concept adopted by many precursors.
Another essential fact to keep in mind for the comprehension of the Horten brothers’ work is to recall the importance that the glider and soaring played in the history of aviation. While many researchers towards the end of the XIXthcentury were trying to create a motorized machine, some purists and grand precursors such as Lilienthal or Ferber believed that a flying machine should be aerodynamically efficient and easy to fly before installing an engine. We must note in passing that Lilienthal had conceived gliders without a tail section before the year 1900.
The Horten brothers would become the virtuosos of the flying wing, testing with stubbornness their machines without neither fuselage nor tail section in gliding flight before even thinking of adapting them with an engine. Obsession? Maybe… Whatever the reasons, they would design flying wings exclusively. No other type of flying machine would come out of their drawing board.
Born at the beginning of the 20th century, the brothers had developed from childhood a passion for the concept of a machine flying with the purest of qualities. The Versailles treaty of 1919 theoretically banned the rearmament of Germany, particularly by drastically limiting its aeronautical production. This is how glider flying and soaring in Germany came to play such an important part between the wars, not only in the training of pilots but also in aeronautical research. The renowned Wasserkuppe meetings would provide the perfect stage for the advancement of those researches.
It is within this time frame that Walter and Reimar Horten developed, and built their first flying wing before reaching the age of twenty after studying the work of von Prandlt (published in 1918) on aerodynamics with the emphasis on the benefits of the thick wing. They also benefited from indulgent parents that allowed them to transform the family’s house living room into a workshop.
During the entire period that preceded the Second World War, the brothers conceived machines having constantly improved performance. Their first glider, the Horten Ho I, was first flight tested at Bonn-Hagelar in July 1933. Although it was not a complete success, it opened the way for other models, including the Ho IV with a high aspect ratio wing of 24 meters in span, as well as their Ho III that soared to 7000 meters in 1938.
When the hostilities began in World War two, the Horten brothers were of course assigned to the Luftwaffe. Wolfram, the third brother was shotdown over Dunkerque flying a Heinkel He-111, whereas Walter flew Messerschmitt Bf-109 for 6 months. Reimar was also trained on the Bf-109 but he was soon transferred to a special unit preparing for operation “Sealöwe” (Operation Sea Lion) having for objective the invasion of England. For this operation the Luftwaffe had created a special glider unit. More than 80 aircraft, had been assigned to this operation to deliver ammunitions and supplies for the troops of the invasion force, it included five Ho III and two Ho II especially equipped for this mission. The third Reich had once again found in the gliding schools a mean of “feeding” its war machine.
We know now that the tenacity and dedication of the British RAF pilots caused the invasion of England to be cancelled indefinitely. The cancellation of operation “Sea Lion” actually benefited the Horten brothers, permitting them to continue their projects, whereas the glider pilot training center was transferred to Königsberg. They concentrated on the repairs of their damaged gliders, and to the development of new models supported by Ernst Udet.
In 1942, the Luftwaffe advised Reimar that it was searching for an aircraft, which they could use to test a Schmitt-Argus pulse jet engine. They asked him if he thought that le Ho V two-seater could serve that purpose. According to certain sources, this decision came about following reports from German spies in the USA regarding the work of Northrop. The Ho V structure did not permit such mean of high thrust propulsion so the Horten brothers returned to the drawing board and conceived a stronger and larger wing. It would be the Ho VII, a machine equipped with two “pusher” type propellers and a pulse jet engine.
This new venture did not stop the brothers from pursuing their fundamental researches. As Etrich in 1908, they would be intrigued by the “flying seed” Zanonia Macrocarpia, which inspired them for the design of their amazing “Parabola”.
But it was wartime and Göering was demanding his “1000X1000X1000”. What was that all about? Nothing else than an airplane capable of transporting on a distance of 1000 kilometers from its base, 1000 kilos of bombs at a speed of 1000 kilometers per hour. It was apparently a very unrealistic project for the era, but one that the Hortens (as well as other German engineers such as those from Focke Wulf) came very close to realizing and make operational.
Six months! That was the maximum time allowed to the brothers to have them conceive a prototype, including the assembly methods. It must be remembered that in 1944 the Luftwaffe was already in a desperate state. The glider prototype was ready in a very short time, built of materials consisting of plywood made with a special solvent resistant glue, and some parts of the machine were even made of composite material. Duraluminum had become a rare strategic material in Germany, and its use would have required highly qualified labor, which had been absorbed to serve on the battlefields.
On March 1st 1944, the Ho IX made its first gliding flight at Göttingen. A second machine had been built to be fitted with turbojet engines. Those turbojets promised for a March delivery were late to be delivered, and when they arrived it was a serious disappointment for the Horten brothers. They had been provided with Jumo 004B of 80 centimeters in diameter, whereas the planned jet engines were not supposed to exceed 60 centimeters! For a more classic machine such as the Me-262, it would not have been an insurmountable problem, but for a flying wing in which the jet engines were to be incorporated, it was a different problem. It would have been necessary to completely redesign the Ho IX, but time no longer permitted such a project. Or, it would have been necessary to substantially increase the wingspan, rendering the airplane unable to achieve the speeds adamantly required by Göering. The Horten brothers therefore resorted to “make do” ingenuity and the machine were ready for test flight at the end of 1944.
Test pilot Lieutenant Erwin Ziller’s logbook shows that the first flight with the turbojet engines took place on February 2nd 1945, but Reimar Horten asserts that December 18th 1944 was the date of this particular flight. The RLM (German Air Ministry) had shown satisfaction with the Ho IX, and giving it the code 8-229 it entrusted its construction to the Gothaer Waggonfabrik works. Twenty of the machine’s first model was ordered. Several other models had been planned, including two-seaters for training, and night fighters equipped with radar. We must note in passing that the Horten brothers had developed a special revetment for their Ho IX, made of glue, soot, and charcoal powder, making this already furtive machine practically undetectable with radar.
On April 14th 1945, the American army arrived at the production factory, capturing the Go 229 (Go for Gothaer the official designation) ending the construction of what had been the first jet propelled flying wing. One of those machines is located at the famed Smithsonian museum.
The Horten brothers did not wait for the arrival of the Americans, and as many of their compatriots, it is in Argentina that they would continue to develop their flying wing. Although they had been geniuses in the conception of airplanes, they had none the less been members of the Nazi party. They went on to design unorthodox gliders, the Horten XV “Urubu” in particular and a giant transport glider the IAME I.A. 28, but only one of this machine was ever built. Disregarding their political involvement more or less doubtful, the Horten brothers remain no less the “grand masters” of the flying wing.
Their stubbornness in their researches resulted in the production of a flying wing possessing great flying qualities, beginning with the first one produced to the last one, even introducing the piloting of the machine in a laying down position to reduce the extra drag produced with a normal canopy configuration. Reimar Horten died in 1994. As for his brother Walter, his life ended in December 1998 in Baden-Baden. And, what else can we say about the Horten brothers’ Go 229 (or Ho IX or Ho 229)? It was a furtive jet propelled flying wing, operational some decades before the F-117 “stealth” the airplane subject of so much publicity during the Gulf War.”
Reimar Horten In Argentina
“Reimar Horten was born in Bonn, Germany on March 12, 1915. He entered into Aeronautics thanks to his brother, who was 28 months older than he was, who built the Ho I when he was 16 years old. It was a one-manned glider without a fuselage, made out of wood and a coated fabric. The experience gained in building the Ho I made it possible to build the Ho II in 1934, and by the following year, it was motorized with an 80 HP Hirt HM 602. In 1938, both of the brothers worked together to construct the Ho III, whose internal body was made up of steel pipes welded together and its external with the traditional structure made of wood coated with fabric. At the beginning of 1939, two famous constructors, Ernest Heinkel and Willy Messerschmitt, wanted to merge their companies with the Horten’s, but the Horten brothers realized that, by accepting this, they would loose their freedom to develop their winged fliers, and for this reason, the rejected both offers.
The Second World War had already started when the German Ministry of Aviation (RLM), working with the Special 9, which was established in Gotingen, gave the Horten brothers the opportunity that they were waiting for and allowed them to build the Ho IV.
The Ho IV was a glider without a fuselage or a motor. It had an elongation of 22 to 1 and it had peculiar design in that the pilot’s entire body was introduced into the plane’s frame lying down. In 1943, with highs and lows in the production of the Ho VII that was equipped with two 240 HP Argus AS 10 C motors, Walter and Reimar -without official authorization- decided to start a new project, the Ho IX, which was a flying wing with a jet-engine. In this unpublished experience, they only had BMW and JUMO motors at their disposition. The development of the 20 pre-production models -with advice from the Horten brothers- was officially authorized by the RLM to the Gothaer Wagonfabrik company, where they titled it the GO-229. Responding to an official job offer, the Horten brothers came to our country in 1948, but two years later, Walter decided to go back to Germany.
Meanwhile, Reimar dedicated himself to the construction of two different glider models (the IA-34 “the Clen Antu” and the IA-41 “Urubu”), a transport (the IA-38), and a jet fighter, all of them being flying wings. On October 19, 1949, the Brig. Juan Ignacio San Martín, who was in charge of the FMA (Fabrication of Military Aviation), presented the secret file 339 with Horten’s project to the Brigadier Cesar Ojeda, the Minister of Aeronautics. The project consisted of a jet fighter with a double delta wing, two drifts on the wings, and internal fuel tanks (four in the wings and one in the cabin). The air intake of the Rolls Royce Derwent V turbine with which the plane was going to be equipped was placed in a ventral form and its internal guns were four 20 mm cannons. Horten planned on reaching higher maximum velocities, lower landing velocities, and have a higher ceiling service than the Pulqui II (the fighter plane with which Kurt Tank was working). Finally, on April 4, 1951, the project was archived, because the Pulqui II’s development was farther ahead and because Argentina could not afford to build two jet-planes at the same time.
Nevertheless, Horten continued working in Argentina, this time on the IA-37, which is also a flying wing, but very different from all of the earlier models. In 1953, he started to do his tests in a wind tunnel, and, under the supervision of Karl Nickel, he made over 200 take offs of models between 5 and 20 kg to test its aerodynamics. Doing this, he reached up to 200 km per hour. In 1954, he built a wooden glider that was presented to the public in March and that flew for the first time on October 1st, which was towed by a Junkers Ju-52. It was later towed by the DC-3 and the Lincoln LV-ZEI (Lincolian, Aries II). Its pilot was the Captain Conan Doyle. It was also a model in which the pilot flew lying down. First Lieutenants Balado, Rossell, and Gonzalez, as well as the German pilot Heinz Scheidhauer participated in the following flight tests.
The flight characteristics were excellent, above all, the take offs and landings were very smooth. It needed very little runway because of its nose that was tilted upward, and because of this, it had a higher front axle. In the models with a motor, they foresaw that the front axle would lift up at a 5 to 25 degree angle during take off and that it would do the opposite during the landing, which would allow the glider to use a shorter runway.
In 1955, Horten started to build a prototype that would use a Derwent V motor, which wasn’t going to allow it to reach the required performance, but it would serve to test different systems. The problem with the motor was that Horten couldn’t get a higher-powered motor in a foreign country, and Argentina wasn’t equipped with the proper equipment to be able to build it. A little later, he was able to upgrade it. In 1956, he changed the position of the pilot from lying down position to a sitting one, and after having recorded 50 hours of flight time with the glider, he started to build the first prototype. In the design, they foresaw the need of a Derwent V motor or two Avon’s, and they believed that it could become a plane with more power, leaving the IA-37 behind as a subsonic trainer. This model, called the IA-48, would be equipped with two Rolls Royce Avon R.A.3 with 2,950 kg of push, two Nene 101 with 2,267 kg of push, or 2 Bristol Orpheus BOr with 2,200 kg of push under the wings, which would have a delta ogival or gothic shape. The plane was believed to be able to reach Mach 2.2.
The Armed Forces were interested in the model, believing that it could be used in their new aircraft carrier that had arrived in 1958, and for this reason, the plane suffered several changes, how the exhaust fumes left the motors. In 1960, when they only needed one more year before they could put the IA-37 into flight, the project was cancelled for lack of funding. This is how Argentina lost out on being able to create their own fighter jet, something that wouldn’t come to take place until 1984, when the IA-63 Pampa flew for the first time.
The Engineer Reimar Horten presented the prototype of what was a tetra-motor flying wing transport. Its construction was begun in 1953. The design was based on the German project of what was the II GM Horten Ho VIII. The prototype was finished in 1959, but the first test flight was delayed because there was a problem in the motors cooling system. Finally, the first flight took place on December 10, 1960, under the command of Major Rogelio Manuel Balado. Towards the end of 1961, the prototype -the only one ever built, – after flying only four times, was abandoned due to unsatisfactory results.
The engine was made up of 4- I Ae 16 “el Gaucho”. It had 9 radial cylinders that put out 450 HP at 2,250 RPM and that turned the propellers, which had a fixed pitch. Originally, they wanted to use a different motor, the IA R-19 R “El Indio”, which put out more HP. The fuel capacity was 1,450 liters, and it was transported in the wings. It was a high-wing monoplane, semi-monocoque, bilarguera structure that was built entirely of duralumin, in an arrow-like form of 36.5 º. It didn’t have a tail unit, and the drifts and rudders were located in the tips of the wings. The landing axle had four principal, fixed wheels and one front wheel that could be retracted into the fuselage. The cockpit, with two seats in tandem, was situated on the edge of the wing. The cargo hold, which was very large, had a capacity of 23 m3, and could transport six tons of cargo. For this reason, it was incorporated with a wide “crocodile mouth” rear door. The bottom part of the “crocodile mouth” was, at the time, used as a ramp when open.
The Dr. and Engineer Reimar Horten died on August 21, 1993, in Villa General Belgrano (Cordoba, Argentina).”
Wingspan: 32 m
Length: 13.50 m
Height: 4.60 m
Wing Area: 133 m2
Gauge: 2.80 m
Weight when empty: 8,500 kg
Useful Cargo: 7,500 Kg
Total Weight: 16,000 kg
Wing Cargo: 120 Kg/m2
Ratio between weight and power: 17.77 kg/HP
Maximum Speed: 252 km/h
Cruising Speed: 215 Km/h
Landing Speed: 140 km/h
Range: 1,250 kilometers
“Horten Ho-229 V3 captured by the United States Army, 1950”
ONLY the WING
12 April 2016
“In his later life, Reimar Horten promoted the idea that the Horten Ho 229 V3 was intended to be built as a stealth aircraft, which would have placed this jet’s design several decades ahead of its time. Reimar Horten claimed that he wanted to add charcoal to the adhesive layers of the plywood skin of the production model to render it invisible to radar, because the charcoal “should diffuse radar beams, and make the aircraft invisible on radar” (Horten and Selinger 1983). This statement was published in his 1983 co-authored book Nurflügel (which translates as “only the wing”). While this statement refers to the never-made production model, it seems possible that the experimental charcoal addition could have been used on the Horten Ho 229 V3 prototype. The mere mention of early stealth technology sparked the imagination of aircraft enthusiasts across the world and spurred vibrant debate within the aviation community.
The British radar station
In 1983, Reimar Horten wrote in Nurflügel that he had planned to combine a mixture of sawdust, charcoal, and glue between the layers of wood that formed large areas of the exterior surface of the Ho 229 V3 production model. This was done to shield, he said, the “whole airplane” from radar as “the charcoal should absorb the electrical waves. Under this shield, then also the tubular steel [airframe] and the engines [would be] invisible [to radar]” (Horten and Selinger 1983, Russ Lee translation). While this statement refers to the never-made production model, it seems possible that the experimental charcoal addition could have been used on the Horten Ho 229 V3 prototype.
In 1943 the all-wing Horten 229 promised spectacular performance and the Luftwaffe (German Air Force) chief, Hermann Göring, allocated half-a-million Reich Marks to the brothers Reimar and Walter Horten to build and fly several prototypes. Numerous technical problems beset this unique design and the only powered example crashed after several test flights but the airplane remains one of the most unusual combat aircraft tested during World War II. Horten used Roman numerals to identify his designs and he followed the German aircraft industry practice of using ‘Versuch,’ literally test or experiment, numbers to describe pre-production prototypes built to test and develop a new design into a production airplane. The Horten IX design became the Horten Ho 229 aircraft program after Göring granted the project official status in 1943 and the technical office of the Reichsluftfahrtministerium assigned to it the design number 229. This is also the nomenclature used in official German documents.
The idea for the Horten IX grew first in the mind of Walter Horten when he was serving in the Luftwaffe as a fighter pilot engaged in combat in 1940 during the Battle of Britain. Horten was the technical officer for Jadgeschwader (fighter squadron) 26 stationed in France. The nature of the battle and the tactics employed by the Germans spotlighted the design deficiencies of the Messerschmitt Bf 109, Germany’s most advanced fighter airplane at that time. The Luftwaffe pilots had to fly across the English Channel or the North Sea to fulfill their missions of escorting German bombers and attacking British fighters, and Horten watched his unit lose many men over hostile territory at the very limit of the airplane’s combat radius. Often after just a few minutes flying in combat, the Germans frequently had to turn back to their bases or run out of fuel and this lack of endurance severely limited their effectiveness. The Messerschmitt was also vulnerable because it had just a single engine. One bullet could puncture almost any part of the cooling system and when this happened, the engine could continue to function for only a few minutes before it overheated and seized up. Walter Horten came to believe that the Luftwaffe needed a new fighter designed with performance superior to the Supermarine Spitfire, Britain’s most advanced fighter. The new airplane required sufficient range to fly to England, loiter for a useful length of time and engage in combat, and then return safely to occupied Europe. He understood that only a twin-engine aircraft could give pilots a reasonable chance of returning with substantial battle damage or even the loss of one engine.
Since 1933, and interrupted only by military service, Walter and Reimar had experimented with all-wing aircraft. With Walter’s help, Reimar had used his skills as a mathematician and designer to overcome many of the limitations of this exotic configuration. Walter believed that Reimar could design an all-wing fighter with significantly better combat performance than the Spitfire. The new fighter needed a powerful, robust propulsion system to give the airplane great speed but also one that could absorb damage and continue to function. The Nazis had begun developing rocket, pulse-jet, and jet turbine configurations by 1940 and Walter’s role as squadron technical officer gave him access to information about these advanced programs. He soon concluded that if his brother could design a fighter propelled by two small and powerful engines and unencumbered by a fuselage or tail, very high performance was possible.
At the end of 1940, Walter shared his thoughts on the all-wing fighter with Reimar who fully agreed with his brother’s assessment and immediately set to work on the new fighter. Fiercely independent and lacking the proper intellectual credentials, Reimar worked at some distance from the mainstream German aeronautical community. At the start of his career, he was denied access to wind tunnels due to the cost but also because of his young age and lack of education, so he tested his ideas using models and piloted aircraft. By the time the war began, Reimar actually preferred to develop his ideas by building and testing full-size aircraft. The brothers had already successfully flown more than 20 aircraft by 1941 but the new jet wing would be heavier and faster than any previous Horten design. To minimize the risk of experimenting with such an advanced aircraft, Reimar built and tested several interim designs, each one moderately faster, heavier, or more advanced in some significant way than the one before it.
The Junkers Jumo 004 jet engine
Reimar built the Horten VC and VC to evaluate the all-wing layout when powered by twin engines driving pusher propellers. He began in 1941 to consider fitting the Dietrich-Argus pulse jet motor to the Horten V but this engine had drawbacks and in the first month of 1942, Walter gave his brother dimensioned drawings and graphs that charted the performance curves of the new Junkers 004 jet turbine engine [this engine was also fitted to these NASM aircraft: Messerschmitt Me 262, Arado Ar 234, and the Heinkel He 162]. Later that year, Reimar flew a new design called the Horten VII that was similar to the Horten V but larger and equipped with more powerful reciprocating engines. The Horten VI ultra-high performance sailplane also figured into the preliminary aerodynamic design of the jet flying wing after Reimar tested this aircraft with a special center section.
Jumo 004C engines mounted in the internal structure of Horten Ho229
Walter used his personal connections with important officials to keep the idea of the jet wing alive in the early stages of its development. General Ernst Udet, Chief of Luftwaffe Procurement and Supply and head of the Technical Office was the man who protected this idea and followed this idea for the all-wing fighter for almost a year until Udet took his own life in November 1941. At the beginning of 1943, Walter heard Göring complain that Germany was fielding 17 different types of twin-engine military airplanes with similar, and rather mediocre, performance but parts were not interchangeable between any two designs. He decreed that henceforth he would not approve for production another new twin-engine airplane unless it could carry 1,000 kg (2,210 lb) of bombs to a ‘penetration depth’ of 1,000 km (620 miles, penetration depth defined as 1/3 the range) at a speed of 1,000 km/h (620 mph). Asked to comment, Reimar announced that only a warplane equipped with jet engines had a chance to meet those requirements.
In August Reimar submitted a short summary of an all-wing design that came close to achieving Göring’s specifications. He issued the brothers a contract, and then demanded the new aircraft fly in 3 months. Reimar responded that the first Horten IX prototype could fly in six months and Göring accepted this schedule after revealing his desperation to get the new fighter in the air with all possible speed. Reimar believed that he had boosted the Reichsmarschall’s confidence in his work after he told him that his all-wing jet bomber was based on data obtained from bone fife flight tests with piloted aircraft. Official support had now been granted to the first all-wing Horten airplane designed specifically for military applications but the jet bomber that the Horten brothers began to design was much different from the all-wing pure fighter that Walter had envisioned nearly four years earlier as the answer to the Luftwaffe’s needs for a long-range interceptor. Henceforth, the official designation for airplanes based on the Horten IX design changed to Horten Ho 229 suffixed with ‘Versuch’ numbers to designate the various prototypes.
All versions of the Ho 229 resembled each other in overall layout. Reimar swept each half of the wing 32 degrees in an unbroken line from the nose to the start of each wingtip where he turned the leading edge to meet the wing trailing edge in a graceful and gradually tightening curve. There was no fuselage, no vertical or horizontal tail, and with landing gear stowed (the main landing gear was fixed but the nose wheel retracted on the first prototype Ho 229 V1), the upper and lower surface of the wing stretched smooth from wingtip to wingtip, unbroken by any control surface or other protuberance. Horten mounted elevens (control surfaces that combined the actions of elevators and ailerons ) to the trailing edge and spoilers at the wingtips for controlling pitch and roll, and he installed drag rudders next to the spoilers to help control the wing about the yaw axis. He also mounted flaps and a speed brake to help slow the wing and control its rate and angle of descent. When not in use, all control surfaces either lay concealed inside the wing or trailed from its aft edge. Parasite or form drag was virtually nonexistent. The only drag this aircraft produced was the inevitable by-product of the wing’s lift. Few aircraft before the Horten Ho229 or after it have matched the purity and simplicity of its aerodynamic form but whether this achievement would have led to a successful and practical combat aircraft remains an open question.
Building on knowledge gained by flying the Horten V and VII, Reimar designed and built a manned glider called the Horten 229 V1 which test pilot Heinz Schiedhauer first flew 28 February 1944. This aircraft suffered several minor accidents but a number of pilots flew the wing during the following months of testing at Oranienburg and most commented favorably on its performance and handling qualities. Reimar used the experience gained with this glider to design and build the jet-propelled Ho 229 V2.
Wood is an unorthodox material from which to construct a jet aircraft and the Horten brothers preferred aluminum but in addition to the lack of metalworking skills among their team of crafts persons, several factors worked against using the metal to build their first jet-propelled wing. Reimar’s calculations showed that he would need to convert much of the wing’s interior volume into space for fuel if he hoped to come close to meeting Göring’s requirement for a penetration depth of 1,000 km. Reimar must have lacked either the expertise or the special sealants to manufacture such a ‘wet’ wing from metal. Whatever the reason, he believed that an aluminum wing was unsuitable for this task. Another factory in Reimar’s choice of wood is rather startling: he believed that he needed to keep the wing’s radar cross-section as low as possible. “We wished”, he said many years later, “to have the [Ho 229] plane that would not reflect [radar signals]”, and Horten believed he could meet this requirement more easily with wood than metal. Many questions about this aspect of the Ho 229 design remain unanswered and no test data is available to document Horten’s work in this area. The fragmentary information that is currently available comes entirely from anecdotal accounts that have surfaced well after World War II ended.”
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